Nowadays natural rubber (one example of polyisoprenoids) for use in industrial rubber products are harvested from isoprenoid-producing plants, such as para rubber tree (Hevea brasiliensis) belonging to the family Euphorbiaceae, or Indian rubber tree (Ficus elastica) belonging to the family Moraceae.
At present, Hevea brasiliensis is virtually the only source for the natural rubber used in industrial rubber products. Hevea brasiliensis is a plant that can only be grown in certain regions, including Southeast Asia and South America. Moreover, Hevea brasiliensis trees take about seven years from planting to grow mature enough to yield rubber, and yields natural rubber only for a period of 20 to 30 years. Demand for natural rubber is expected to grow in the future, especially in developing countries, but for the reasons discussed above it is difficult to greatly increase natural rubber production from Hevea brasiliensis. There is therefore concern that natural rubber sources will dry up, and needs exist to develop stable natural rubber sources other than mature Hevea brasiliensis trees and to improve productivity of natural rubber from Hevea brasiliensis. 
Natural rubber has a cis-1,4-polyisoprene structure, with isopentenyl diphosphate (IPP) unit, and the nature of this structure suggests that cis-prenyltransferase (CPT) is involved in natural rubber biosynthesis. For example, several CPTs are found in Hevea brasiliensis, including Hevea rubber transferase 1 (HRT1) and Hevea rubber transferase 2 (HRT2) (see, for example, Non Patent Literatures 1 and 2). It is also known that rubber synthesis can be reduced in the dandelion species Taraxacum brevicorniculatum by suppressing CPT expression (see, for example, Non Patent Literature 3).
Previous studies of proteins associated with natural rubber biosynthesis have focused on rubber elongation factor (REF) and small rubber particle protein (SRPP) (see, for example, Non Patent Literatures 4 and 5). However, the associations between these proteins and CPT are not completely understood.
It has also been suggested that Nogo-B receptor (NgBr) is involved in dolichol biosynthesis by a human CPT (see, for example, Non Patent Literature 6).